Insertion of a needle into the spinal canal through the midline of the back is an established medical procedure. The purpose of such a needle insertion is (1) to obtain a sample of spinal fluid for analysis, (2) to inject medications or contrast media as in x-ray examinations, or (3) to inject local anesthetic solutions for surgical anesthesia, pain control or diagnostic procedures.
A complication of this procedure is the so-called post spinal tap headache. The purpose of this invention is the prevention of this complication.
The spinal canal begins at the base of the skull and extends downward, encased in the vertebral column, to the sacrum. It contains the spinal cord which is an extension of the brain stem. It terminates at approximately the 1st lumbar vertebra. It also contains the spinal nerves which extend from the cord to points of exit from the canal. The spinal canal is filled with a fluid which at its upper limit is continuous with a similar system that encases the brain, the fluid systems being the same and serving the same purpose: cushioning the nerve tissues they contain.
To enter the spinal canal, needle insertion is usually below the level of the 1st lumbar vertebra so as not to strike the spinal cord. Traversing the skin, subcutaneous tissues and fascial planes produces no lasting untoward effect. However, when the needle enters the dura and pia mater a hole is produced which, because of the fibrous nature of the dura, tends to remain open after the needle is withdrawn. Spinal fluid leaks out of this hole into the surrounding tissues and is absorbed. As spinal fluid is lost, the cushioning effect on the nerve tissues of the system also is lost. The resulting hypovolemia of spinal fluid makes itself apparent when the subject of the spinal tap goes from the supine to erect position. All the tissues of the canal system including the brain gravitate downward due to the lack of spinal fluid cushion. As the brain gravitates down, pull on structures attached to the brain and skull produce pain which is interpreted by the subject as headache, usually severe and incapacitating.
The cause of the headache following spinal tap is the hole produced in the dura mater at the time of needle insertion. This invention seeks to seal the hole on needle withdrawal so that loss of spinal fluid is prevented.